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The pixel ionisation chamber: a detector for beam monitor and dosimetry

The pixel ionisation chamber: a detector for beam monitor and dosimetry. A.Boriano 1,2 , F.Bourhaleb 2,3 , R. Cirio 2 , M. Donetti 2,4 , F. Marchetto 2 , C. Peroni 2 , C.J. Sanz Freire 2^ 1 ASP, Torino, Italy 2 University and INFN, Torino, Italy

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The pixel ionisation chamber: a detector for beam monitor and dosimetry

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  1. The pixel ionisation chamber: a detector for beam monitor and dosimetry A.Boriano 1,2, F.Bourhaleb 2,3, R. Cirio 2, M. Donetti 2,4, F. Marchetto 2, C. Peroni 2, C.J. Sanz Freire 2^ 1 ASP, Torino, Italy 2 University and INFN, Torino, Italy 3 ICSC WorldLab, Lausanne, Switzerland 4 TERA Foundation, Novara, Italy ^ partially supported by IBA, Louvaine- la-Neuve, Belgium PTCOG XXXV – PMRC Tsukuba – November 15 2001

  2. Improving the Magic Cube (3D dosimeter for hadron beams) The IBA Magic Cube at NPTC in Boston The Magic Cube can be bought at Physalus (furio.gramatica@physalus.it) Roberto Cirio INFN Torino

  3. The pixel chamber • parallel plate ionization chamber • anode segmented in 1024 square pixels • pixel dimension = 7.5 X 7.5 mm2 • sensitive area = 24 X 24 cm2 • 1 mm water equivalent thickness • front-end electronics, located around the chamber, perform analog to digital conversion Roberto Cirio INFN Torino

  4. Front-end electronics • located around the chamber • we have developed a full custom chip (TERA05) • every chip has 64 channels that convert the collected charge in digital output Roberto Cirio INFN Torino

  5. TERA05 channel # 1 channel # 64 • Very Large Scale Integration (VLSI) • if conversion • output  Qint • 100 fC<charge quantum<800 fC • Imax= 4 A • 64 channels • 16 bit wide counters • multiplexed digital output • dead-time free readout • max read out = 10 MHz Roberto Cirio INFN Torino

  6. Linearity at 100 fC charge quantum • 20 pA < I < 0.6 A • Linearity better than 0.7 % Roberto Cirio INFN Torino

  7. Linearity at 600 fC charge quantum • 10 pA < I < 2 A • Linearity better than 0.3 % Roberto Cirio INFN Torino

  8. Spread of charge quanta RMS  1 % • I = 49.96 nA • 26 chips Roberto Cirio INFN Torino

  9. Reproducibility of charge quantum • I = 49.96 nA • Qc = 600 fC • 24 ºC < T < 27 ºC • 1 month • 6 measures Roberto Cirio INFN Torino

  10. Data acquisition <100 m • connection detector-data acquisition by twisted pair flat cables (100 m maximum lenght) • max rate transfer = 10 MHz = 40 Mb/s • read out transfer time = 50 s • read out cycle total time = 100 s • real time operating system Roberto Cirio INFN Torino

  11. Beam test at GSI • Beam characteristics • raster-scan delivery system • 270 MeV/u, C+6, 8.8 mm (FWHM) • data acquisition synchronized with raster-scan • Aims • spatial resolution • homogeneity of response Roberto Cirio INFN Torino

  12. Spatial resolution Spatial resolution  < 0.2 mm Roberto Cirio INFN Torino

  13. Homogeneity of response 18 × 18 cm2 uniform field  = 2.0 %  = 1.1 % Roberto Cirio INFN Torino

  14. Beam test at PSI • Beam characteristics • spot-scan delivery system • 138 MeV/u, p, 7 mm (FWHM) • data acquisition non-synchronized with spot-scan • Aims • Intercomparison Roberto Cirio INFN Torino

  15. Comparison with PSI proton beam transverse profile Roberto Cirio INFN Torino

  16. …very good for IMRT with photons too …!(cfr. collaboration with IBA/Wellhofer/Scanditronix) Field shape varying with time 6 MV Elekta accelerator at S.Anna hospital in Torino 1.2x1.2 cm2 square field going to 12.4x12.4 cm2 square field Roberto Cirio INFN Torino

  17. Conclusions • parallel plate pixel ionization chamber • big sensitive area • 1024 independent measurements • VLSI electronics dead-time free readout • one dead-time free readout of all 1024 channels every 100 s • GOOD MONITOR FOR SCANNED BEAMS • Next step might be a real-3D-Magic Cube ( dosimeter) Roberto Cirio INFN Torino

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